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Computer Network Assignment A131779
INTRODUCTION A computer network, often simply referred to as a network, is a group of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources. Networks may be classified according to a wide variety of characteristics. A computer network allows sharing of resources and information among interconnected devices. In the 1960s, the Advanced Research Projects Agency (ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. It was the first computer network in the world. Development of the network began in 1969, based on designs developed during the 1960s. 'Purpose' Computer network is a system consisting of computers, software and device networking others working together to achieve a common purpose. The purpose of the computer network are: *Dividing resources: for example the use of shared printers, CPUs, memory, hard drive *Communication: eg electronic mail, [http://id.wikipedia.org/wiki/Instant_messaging instant messaging], [http://id.wikipedia.org/wiki/Chatting chat] *Access to information: for example [http://id.wikipedia.org/wiki/Web web] [http://id.wikipedia.org/w/index.php?title=Browsing&action=edit&redlink=1 browsing] In order to achieve the same goal, each part of the computer network to request and provide services (service). Parties who request / receive services is called a client (client) and which give / send a service called the waiter (server). Architecture is called the system a client-server, and used in almost all applications of computer networks. BACKGROUND History of Computer Networks The concept of computer network born in the 1940s in America of a development project in the laboratory computer MODEL I Bell and Harvard University research group led by professor H. Aiken. At first the project was to utilize a computer device that must be used together. To do some of the process without much waste of time was made vacant succession process (batch processing), so some programs can run on a computer with the rules of the queue. In the1950s when the types of computers began to swell up to the creation of a super computer, a computer must serve several terminals (see Figure 1) For that discovered the concept of distribution of time-based process known as TSS (Time Sharing System), for the first time form network (network) computer application. In the TSS system several terminals connected in series to a host computer. In the process of TSS began to seem a mix of computer technology and telecommunication technology that was originally developed on their own. Figure 1 Network model computer TSS Entering the 1970s, after much work load increased and the price of computers began to seem very expensive, then start to use the concept of the distribution process (Distributed Processing). As in Figure 2, in this process some of the host computer to do a great job in parallel to serve several terminals are connected in series in each host computer. Dala distribution process is absolutely necessary in-depth blend of computer and telecommunications technology, because in addition to the process that must be distributed, all must serve the host computer terminals in a single command from the central computer. Figure 2 models of distributed processing computer network Furthermore, when the small computer prices have started to decline and the concept of the distribution process has matured, then the use of computers and networks have started a variety of start dealing with the process and communication between computers (Peer to Peer System) alone without going through a central computer. For that began developing the local network technology known as the LAN. Similarly, when the Internet was introduced, the majority of stand-alone LAN began an association and forming a giant network WAN. BENEFITS Following are some of the advantages of computer networks: *'File Sharing: '''Networks offer a quick and easy way to share files directly. Instead of using a disk or USB key to carry files from one computer or office to another, you can share files directly using a network. *'Software Cost and Management: Many popular software products are available for networks at a substantial savings in comparison to buying individually licensed copied for all of your computers. You can also load software on only the file server which saves time compared to installing and tracking files on independent computers. Upgrades are also easier because changes only have to be done once on the file server instead of on individual workstations. *[http://www.spamlaws.com/wireless.html '''Security]: 'Specific directories can be password protected to limit access to authorized users. Also, files and programs on a network can be designated as "copy inhibit" so you don’t have to worry about the illegal copying of programs. *'Resource Sharing: 'All computers in the network can share resources such as printers, fax machines, modems, and scanners. *'Communication: 'Even outside of the internet, those on the network can communicate with each other via electronic mail over the network system. When connected to the internet, network users can communicate with people around the world via the network. *'Flexible Access: 'Networks allow their users to access files from computers throughout the network. This means that a user can begin work on a project on one computer and finish up on another. Multiple users can also collaborate on the same project through the network. *'Workgroup Computing: '''Workgroup software like Microsoft BackOffice enables many users to contribute to a document concurrently. This allows for interactive teamwork NETWORK CLASSIFICATION The following list presents categories used for classifying networks. '''Connection method Computer networks can be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as optical fiber, Ethernet, wireless LAN,HomePNA, power line communication or G.hn. Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges, or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium. ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network. Based on the distribution of sources of information / data 'Centralized network' This network consists of client and server computer where the client computer that serves as an intermediary to access sources of information / data derived from a single computer server. A centralized network is one where each computer or workstation in the network connects to the central server with its own connection cable. A centralized network has a star topography, with the server in the center and cables radiating out to the computers. In many centralized networks, the computers connected to the server are dumb terminals. The dumb terminals don't have any actual computing capabilities; they're simply monitors that display the programs and data running on the server. 'Distributed Networks' A mix of some centralized network so that there are several computer servers that are interconnected with the client to form a specific network system. 'Decentralized Networks' A decentralized network, which is similar to many of the LANs (local-area networks) in use today, consists of several servers that all connect to each other. A few computers then connect to a single server. The individual computers have access to other servers through the server to which they connect. Based on geographic coverage can be divided 'LAN (Local area network)' A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines).[2] Typical library network, in a branching tree topology and controlled access to resources. All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers. The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.[3] ''Personal area network A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters.[4] A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN. Home area network A home area network (HAN) is a residential LAN which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a CATV or Digital Subscriber Line (DSL) provider. It can also be referred as an office area network (OAN). 'WAN (Wide area network) A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Campus network A campus network is a computer network made up of an interconnection of local area networks (LAN's) within a limited geographical area. The networking equipments (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.). In the case of a university campus-based campus network, the network is likely to link a variety o/f campus buildings including; academic departments, the university library and student residence halls. '''MAN (Metropolitan area network) A Metropolitan area network is a large computer network that usually spans a city or a large campus. ''Enterprise private network'' An enterprise private network is a network build by an enterprise to interconnect various company sites, e.g., production sites, head offices, remote offices, shops, in order to share computer resources. Sample EPN made of Frame relay WAN connections and dialup remote access. ''Virtual private network A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features. ''Sample VPN used to interconnect 3 offices and remote users A VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point. ''Internetwork An internetwork is the connection of two or more private computer networks via a common routing technology (OSI Layer 3) using routers. The Internet is an aggregation of many internetworks, hence its name was shortened to Internet. *'Backbone network''' 'Global area network' A global area network (GAN) is a network used for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.[5] 'Internet' The Internet is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network(ARPANET) developed by DARPA of the United States Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW). Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths. 'Intranets and extranets' Intranets and extranets are parts or extensions of a computer network, usually a local area network. An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information. An extranet is a network that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities—a company's customers may be given access to some part of its intranet—while at the same time the customers may not be considered trusted from a security standpoint. Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although an extranet cannot consist of a single LAN; it must have at least one connection with an external network. 'Overlay network' An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay are connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. A sample overlay network: IP over SONET over Optical For example, many peer-to-peer networks are overlay networks because they are organized as nodes of a virtual system of links run on top of the Internet. The Internet was initially built as an overlay on the telephone network .[6] Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines usingmodem, before any data network existed. Nowadays the Internet is the basis for many overlaid networks that can be constructed to permit routing of messages to destinations not specified by an IP address. For example, distributed hash tables can be used to route messages to a node having a specific logical address, whose IP address is not known in advance. Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees to achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP Multicast have not seen wide acceptance largely because they require modification of all routers in the network.[citation needed] On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers. The overlay has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes a message traverses before reaching its destination. For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes End System Multicast and Overcast for multicast; RON (Resilient Overlay Network) for resilient routing; and OverQoS for quality of service guarantees, among others. Based on the role and relationship of each computer in data processing 'Client-Server Networks' In this network there are 1 or more server computers and client computers. Computers that will be a computer server or a client computer and can be switched through the network software protocol. The client computer as an intermediary to be able to access data on a server computer while the computer server providing the information required by the client computer. An example is a domain such as www.detik.com served by many web server computer. Or it could be a lot of service / services provided by a single computer. Examples are jtk.polban.ac.id servers that constitute a computer with a multi-service namely mail server, web servers, file servers, database servers and others. 'Peer-to-peer Networks' In this network there are no client computer and server computer because all computers can perform transmission and reception of information so that all computers function as clients as well as the server. For example in file sharing between computers on the Network Windows Network Neighbourhood there are 5 computers (we named A, B, C, D and E) that gives the right of access to the files they have. At one point A from B to access a file share named data_nilai.xls and also gives access to the files soal_uas.doc C. When A access the files from B then A serves as a client and when A gives access to the file C then A serves as a server. Both functions were performed by A at the same time, the network like this is called peer to peer. Based on data transmission media 'Wired Networking (Wired Network)' In this network, to connect one computer to another computer in the form of liaison required cable network. Network cable to function within sends information in the form of signal power between the network computer. 'Wireless Networking (WI-FI)' A network with medium in the form of electromagnetic waves. In this network is not required cable to connect between computers because it uses electromagnetic waves which will transmit signals between a computer information network. 'Network topology' Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks. Computer networks may be classified according to the network topology upon which the network is based, such as: *Bus Topology - In two unjung bus topology network must be terminated with a terminator. Barrel connector can be used to expand them. The network consists of only one cable channel that uses a BNC cable.Computers that want to connect to the network to associate himself with mentap Ethernet over cable. *Ring topology - a network topology in the form of a series of dots, each connected to two other points, such that form a circular path to form a ring. In the ring topology, data communication can be disrupted if a single point crash. FDDI Network anticipate this weakness by sending data clockwise and counterclockwise with clockwise direction simultaneously. [learn more...] *Mesh Topology - a form of relationship between devices where each device is connected directly to other devices in the network. Consequently, in a mesh topology each device can communicate directly with the target devices (dedicated links). Thus the maximum number of connections between devices on the network bertopologi this mesh can be calculated that as many as n (n-1) / 2. Also because every device can connect with other devices on the network, each device must have as many as n-1 Port Input / Output (I / O ports). Based on the above understanding, it can be exemplified that when as many as 5 (five) computers will be connected in a mesh topology so that all connections between computers to function optimally, it needs a connection cable 5 (5-1) / 2 = 10 connection cable, and each each computer must have a port I / O as much as 5-1 = 4 ports. [learn more...] *Tree Topology - Network Topology Tree (Tree) network topology is also called multilevel network topology. This topology is usually used for interconnection between different central denganhirarki. For the lower hierarchy depicted in locations that are low and getting older has the higher hierarchy. This type of network topology suitable for use on a computer network system. [learn more...] *Linear Topology- a computer network with linear topology usually called linear bus topology, this layout includes a general layout. One main cable connecting each connection point (computer) connected with a connector called T Connector and the ends must be terminated with a terminator. BNC-type connectors used (British Naval Connector), actually is the name of BNC connectors rather than the name of the cord, the cable used is RG 58 (Cable Coaxial thinnet). Installation of linear bus topology is very simple and inexpensive, but most consist of 5-7 computers. [learn more...] *Star Topology - a form of network topology in the form of convergence of the node center to each node or user. Star network topology including network topology with high costs.[learn more...] BASIC HARDWARE COMPONENTS All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable ("optical fiber"). 'Network interface cards' A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. 'Repeaters' A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. Repeaters work on the Physical Layer of the OSI model. 'Hubs' A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address.[7] It works on the Physical Layer of the OSI model. 'Bridges' A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges broadcast to all ports except the port on which the broadcast was received. However, bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address to that port only. Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived. Bridges come in three basic types: *'Local bridges': Directly connect local area networks (LANs) *'Remote bridges': Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers. *'Wireless bridges': Can be used to join LANs or connect remote stations to LANs. 'Switches' A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets.[8] A switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected. A switch breaks the collision domain but represents itself as a broadcast domain. Switches make forwarding decisions of frames on the basis of MAC addresses. A switch normally has numerous ports, facilitating a star topology for devices, and cascading additional switches.[9] Some switches are capable of routing based on Layer 3 addressing or additional logical levels; these are called multi-layer switches. The term switch is used loosely in marketing to encompass devices including routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). 'Routers' A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet (Internet protocol information from Layer 3 of the OSI Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known as the "black hole" interface because data can go into it, however, no further processing is done for said data). REFERENCE OF OSI MODEL AND STANDARDIZATION To organize a variety of computer vendor communications needed a rule that the standard and disetejui various parties. Just as two people of different nations, to communicate need a translator / interpreter or a language understood by both parties. In the world of computers and telecommunications is identical to the protocol interpreter. For that the world body dealing with standards of ISO (International Standardization Organization) make the rule known as the OSI reference model (Open Systems Interconnection). It is expected all vendors of telecommunications equipment must be guided by this reference model in developing the protocol. OSI reference model consists of 7 layers, ranging from physical layer up to the application. This reference model is not only useful for LAN products, but in the Internet network build even really needed. The relationship between the OSI reference model with an Internet protocol can be seen in Table 1. Table 1. OSI reference model relationship with the Internet protocol Standardization of network problems is not only done by ISO alone, but also held by other world bodies such as ITU (International Telecommunication Union), ANSI (American National Standards Institute), NCITS (National Committee for Information Technology Standardization), even by the professional associations IEEE (Institute of Electrical and Electronics Engineers) and the ATM-Forum in the Americas. In practice even the vendors of LAN products produced even using the IEEE standard. We can see such body established by the IEEE working a lot to make the standardization of telecommunications equipment as shown in Table 2. Table 2. Agency workers in the IEEE CONCLUTIONS This course teaches students how to understand the basics of computer networking technology today. Broadly speaking, this course discusses the concept of a layer of the OSI and TCP / IP implementations as a reference base computer network technology. The discussion starts from the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and finally the application layer. See Also about... 'Ethernet' Ethernet is a networking system that created and patented the company Xerox. Ethernet is an implementation method CSMA / CD (Carrier Sense Multiple Access with Collision Detection) which was developed in 1960 on the wireless project at the Hawaii University ALOHA over coaxial cable. Standardization of Ethernet systems conducted since 1978 by the IEEE. (See Table 2.) Speed of data transmission in ethernet so far is 10 to 100 Mbps. While in general the market is the speed of 10 Mbps ethernet is commonly called 10Base series. There are various types 10Base are: 10Base5, 10Base2, 10BaseT, and 10Base-F which will be explained further later. In the method CSMA / CD, a host computer that sends data to the network to first ensure that the network is not used for transfers from the host computer and other. If at this stage of checking and found another data transmission in a collision (collision), then the host computer is required to repeat the request (request) delivery on the next time interval which was randomly (random). Thus, effective networking can be used interchangeably. To determine the position where a host computer is located, then each device is given Ethernet address (address) along the 48-bit unique (only one in the world). Address information is stored in a chip that typically appears during the computer in the start sequence of numbers in base 16, as in Figure 3. Hardware CPU (Central Processing Unit): CPU or central processing unit relates to a specific or processor. The performance of the computer is determined by the CPU chip (processor speed) and the other computer circuitry. Currently, the Pentium chip (processor) is the most popular even though there are other chips available in the market today such as AMD, Motorola and others. The clocks speed becomes most important factor in determining the performance of a computer. The motherboard contains the hardware circuitry and connections that allow the different hardware components of the PC to interact and communicate with each other. Most computer software is being developed for the latest processors so it would be difficult to use the older systems. Hard Disk Drives – Disk drive is the mechanism to run the disks. All disks need a drive to get the information, read it and put it back to the disks. Hard disk is used to store the data permanently. Often the terms disk and drive used to describe the same thing but it should be clear that a disk is a storage device. Modem – A modem is used for the modulation and demodulation of the data that is transferred through the modem and the telephone lines. Modem translates the data from digital to analog from analog to digital. Because on the telephone lines data can travel in the form of the analog signals and in the computer data transmits in the form of digital signals. Modems are measured by the speed which is called baud rate. The typical baud rate is 56Kb. Keyboard – The keyboard is used to type something or input information to the computer. There are different designs and models of the keyboards in the market. The most common layout of the keyboard is QWERTY layout. A standard keyboard has 101 keys and embedded keys. Video cards-Video cards allow computer to display video, graphics and animation. Some video cards allow computers to display television. A video card with a digital video camera allows users to produce live video. A high speed broadband internet connection is required to watch the videos on net. Network cards: Network interface cards allow PCs to connect with each other and communicate. Every network computer is required to have a NIC card. NIC cards are required both in wired and wireless networking. Cables: There are two broad types of cables internal cables, which are embedded on the mother board circuit that performs the communication between the devices and CPU. The other types of the cables are the network cables like coaxial cable, CAT 5, Ethernet cables. These cables are used for the communication purposes between the devices or computers. Memory – Memory is the one of the important piece of the hardware. Sometimes memory chip memory is confused with the hard disk memory. Sometimes unallocated space of the hard disk is used as virtual memory also known as page file. This type of memory is a temporary memory and is used actual memory is less and requires some additional memory to perform a specific task. RAM (Random Access Memory) RAM is a memory that is being used by the computer to store the information temporarily. For example when some work is performed on some applications that work is temporarily stored in the RAM. More RAM in the computer more faster computer works. Today at least requirement of a modern PC is 64 RAM. RAM is in the form of a chip and different vendors have developed the RAM of different capacities. Mouse – Every modern computer requires a mouse for faster operations. Generally a mouse has two buttons left and right to perform different functions. One type of the mouse has a round ball under the bottom. Another type of the mouse use optical system to track the movement of the mouse. Monitors – The monitor is used to display the information on the screen. All the activities of a computer, functions and tasks are seen on the computer screen and this is called outputting information. Monitors come in many sizes and shapes, monochrome or full colors. Today most computers use LCD screens. It is light weight and consumes less power as compared to the monitors. Printers – The printer takes the information from the PC and transfers it to the paper of different sizes, which are placed in the printer device. There are three basic types of a printer such as dot matrix, inkjet and laser. Scanners- Scanners allow you to transfer pictures and photographs to your computer. A scanner is used to scan the images and pictures. You can then send the image to someone, modify it or take a print out of it. With optical character recognition software you can convert printed documents into the text that you can use in the word processor. Digital camera- You can take the digital photographs with the digital cameras. The images are stored on the memory chip of the digital cameras and you can transfer them to your computer with the USB drive. Case – Case or casing covers the whole computer’s circuitry. There are two types of casings desktop and tower casing. There is room inside the casing to add or remove components. Cases come in many sizes like desktop, mini, midi and tower. There are some additional empty slots inside the cases such as IDE, USB, ASI, PCI and firewire slots. Cards – Cards are the hardware components that are added to the computer to increase their functionalities and capabilities. Sound cards produce the sound like music and voice. The older cars were 8, 16 and then 32 bits. Color cards allow computers to produce colors. Initially there were 2, 4 and then 16 bits. The main types of the graphic cards are EGA, VGA and SGA. The 32 cards are the standard to display almost billions of the colors on the monitor. REFERENCES http://fadel05.tripod.com/network/jaringan.html#jaringan http://www.buzzle.com/articles/computer-networking/ http://en.wikipedia.org/wiki/Computer_network http://id.wikipedia.org/wiki/Jaringan_komputer